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Next European Dipole Insulation Development
Simon Canfer, Elwyn Baynham, George Ellwood
HHH Highlight Presentation at CERN, November 2005
Simon Canfer
Slide 2
Contents
• NED• State of the art Niobium-tin
insulation• Scope of work• Sizing• Testing programme• Radiation issues
Simon Canfer
Slide 3
Next European Dipole• R&D on advanced accelerator
magnet technology for existing and future facilities
• A European effort to bring niobium-3 tin technology to maturity and to boost the competitiveness of European laboratories and industry
• Wind-and-react niobium-3 tin 15 Tesla 88mm bore dipole, to enable LHC upgrades
Simon Canfer
Slide 4
NED is a Research Activity within CARE
• WP1 Management and communication• WP2 Thermal Studies and Quench
Protection• WP3 Conductor Development• WP4 Insulation Development and
Implementation• Working Group on Magnet Design and
Optimization
Simon Canfer
Slide 5
NED Participating Labs and Institutes
• CCLRC, UK• CEA, France• CERN• CIEMAT, Spain• INFN-Milan, Italy• INFN-Genova, Italy• Twente University, Netherlands• Wroclaw University, Poland
Simon Canfer
Slide 6
Niobium-tin insulation for wind-and-react: current method
• No organic material as it degrades during niobium-tin heat treatment
• Remove organic glass sizing by heating in air• Some labs use palmitic acid as a lubricant
“resizing”• Wrap superconductor cable with glass fibre tape
– Desized glass is fragile!
• Wind coil• Heat treatment typically 660 C for some days
argon/vacuum• Vacuum impregnation with an epoxy• Cure, demoulding
Simon Canfer
Slide 7
What should NED Insulation work package focus on?
• Greatest challenge is Industrialisation of niobium-tin dipole production, eg for large number of s-LHC dipoles
• Cable wrapping is currently a problem – fragile desized glass fibre tape tears
• …so sizing is desirable but commonly-used sizings are not suitable for this application
• If the sizing issue can be overcome then mass-production will be easier
Simon Canfer
Slide 8
Scope of NED Insulation Development
• Write Insulation Specification • Address the sizing issue• Search for alternatives• Use screening tests to economically
assess alternatives• Investigate effect of applied stress
during vacuum impregnation• Radiation studies
Simon Canfer
Slide 9
Screening test methods
• 4 Key tests chosen for screening of materials and process changes:
1. Interlaminar fracture test used to determine Work of Fracture (ASTM5528)
• Literature exists on low temperature application - Shindo
2. Short-beam-shear (ASTM D2344)
• At 77K, tests fibre-to-matrix bond
3. Electrical breakdown strength BS7831
• carbon residues from degraded organic material, e.g. sizing
4. Colour of composite • evidence of carbon residues
Interlaminar fracture
Short-beam shear
Simon Canfer
Slide 10
High temperature sizing
• Literature survey found a polyimide sizing
• Rated to 500ºC in air• Passes key NED specifications after
660 º C in vacuum:1. Work of fracture better than S glass control 2. Shear strength 100MPa3. Electrical breakdown strength >30kV/mm4. Composite is light in colour (indicating little or
no carbon residue)
Simon Canfer
Slide 11
Work of fracture testing
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
G k
J/m
2
Fibre breakage
•Heat-treated S-glass with Polyimide sizing gives higher work of fracture than control
•Epoxy resin = DGEBF/DETDA for all tests
Simon Canfer
Slide 12
S Glass Fracture surfaces
Scale:mm
Broken fibresNo heat treatment- interlaminar failure
Desized, heat treated Translaminar
Simon Canfer
Slide 13
SEM – Fracture Surfaces
Desized/heat treated S-glass – note broken fibres
Polyimide sizing – fibres relatively intact
Simon Canfer
Slide 14
Vacuum impregnation under applied stress
• Why? Because some stress is required to maintain accurate coil geometry
• Excessive stress is known to cause an opaque laminate
• We have vacuum impregnated glass cloth in a vacuum bag under stress, cured under stress, and measured short-beam-shear strength at 77K
Simon Canfer
Slide 15
Effect of applied stress on Short-Beam-Shear Strength
Force applied by an acrylic block, to enable viewing of impregnation
• High stresses (to date up to 10 MPa) did not stop impregnation
• GRP appeared white only after curing
50mmepoxy resin
vacuum
Simon Canfer
Slide 16
Effect of applied stress on Short-Beam-Shear Strength
0
20
40
60
80
100
120
140
160
0 2 4 6 8 10
Impregnation Stress (MPa)
SB
S (
MP
a)
Simon Canfer
Slide 17
Opacity is a good guide to laminate strength
transparent
opaque
SBS (MPa)
116
110
102
72
47
34
Simon Canfer
Slide 18
Radiation issues• LHC IR upgrade - very high heat
and radiation loads (up to 500MGy) - makes cos-theta design impractical for an organic insulation
• USA (LARP) working on an “open-midplane” design, reduces heat loads from 50mW/g to <1mW/g.
• Heat absorbed in tungsten rods at 77K
• S-LHC (energy upgrade) dipoles - far lower radiation loads, conventional cos-theta design more realistic (1000+ magnets)
Mohkov, CARE meeting March 2005
Simon Canfer
Slide 19
Radiation testing
• Need an irradiation test facility with realistic spectrum (50% hadrons) at low temperatures
• Why realistic spectrum? – High energy hadrons are more damaging to
organic insulation materials than gamma
• Why low temperatures?– At low temperatures evolved species (H2, CH3
etc) are frozen into the organic matrix.– On warming the trapped gases can be
damaging
Simon Canfer
Slide 20
Thin S-glass and quartz tapes
• Total turn-to-turn insulation thickness 0.4mm max, so 0.1mm tape required. Not standard products
• JPS Composites Inc. have woven specially thin S-glass and quartz for NED, down to 0.06mm
• Meets NED insulation thickness specification ATLAS conductor + 2 * 0.1mm thick
S-glass tape
Simon Canfer
Slide 21
Conclusions
• Polyimide sizing offers improved materials properties for Nb3Sn insulation
• High stresses during resin impregnation and cure reduce shear strength
• Thanks to: – Hydrosize Technologies Inc. – supplier of polyimide sizing– JPS Composites – weaver and supplier of S-glass and
quartz with polyimide sizing – This work is supported in part by the European Community-
Research Infrastructure Activity under the FP6 "Structuring the European Research Area" (CARE, contract number RII3-CT-2003-506395)